The present invention relates to the write driver circuit for a hard disk drive (HDD). More particularly, it relates to a hard disk drive write head and circuits for adjusting the overshoot of the write head drive current to optimize the rise time and fall time and other characteristics of the write to disk operation.
A hard disk drive storage system typically includes one or more rotating disks, or platters having magnitizible material coated on their surfaces. Read/write heads associated with each platter surface move together radially across the head to reach addressable data regions located on concentric circles called tracks. It is now common to have separate read and write heads. The write head is essentially a small coil of wire which stores data by magnetizing small regions of the disk platter along the tracks. A current driven through the write head creates a temporary magnetic field which magnetizes a small region of the disk at the current position of the write head.
The electronic circuitry used to drive current through the write head typically uses an H-bridge as shown in FIG. 1. For example, U.S. Pat. No. 6,638,012, issued to Hashimoto et al. and incorporated herein by reference, uses an H-bridge for a write driver circuit. The purpose of the H-bridge is to allow electric current to be driven through the write head in either direction. When the current is driven in one direction a magnetic field is created with the north pole in one direction, and when the current is driven in the opposite direction, a magnetic field is created with the north pole in the opposite direction. The H-bridge operates to switch the drive current through the head by turning on a pair of transistors to allow current to flow in a path from a supply source to ground. For example, current flows through the write head from Hx to Hy when transistors Y are turned on and transistors {overscore (Y)} are turned off. Similarly, current flows the opposite direction when transistors {overscore (Y)} are turned on and transistors Y are turned off. The tr, tf (rise time, fall time) is the time corresponding to the speed at which current can reverse through the inductive load of the HDD write head.
It is desirable to increase the speed of the change of current flow to increase the amount of data that can be stored on a single track of the HDD platter. A limitation to decreasing the tr, tf is the amount of overshoot. FIG. 2 illustrates the current waveform for a test input to a typical prior HDD write head. As the switching speed of the current through the head in increased, an overshoot 20 is produced at the head. While some overshoot can be tolerated, too much overshoot in some applications can have deleterious effects on the head and consequently the overall drive system performance.
The prior art circuit provided enhanced overshoot by adding capacitors 16, 18 as shown in FIG. 1. In this circuit, at the beginning of the drive cycle, additional current is dumped to the write head nodes through the capacitors 16, 18.
The present invention provides an improved write drive circuit which allows the adjustable control of the overshoot transients of an H-bridge head drive circuit. In one embodiment, the invention provides an adjustable capacitor in the head driver circuits to selectably determine the current injected to the head drive during the switching transient period. The variable capacitor may be controlled through the serial input to the pre-amp device to allow programmability of the overshoot characteristics for the hard disk drive.
In another embodiment of the present invention, an adjustable overshoot circuit includes a variable capacitor having several capacitors arranged in parallel and selectably connected to the circuit with the final metalization layers of the integrated circuit.
In yet another embodiment, there is provided an adjustable current inverter in conjunction with a fixed capacitor to drive the H-bridge transistors. The adjustable current inverter may comprise several transistors with individual control inputs. These controlled transistors can be used to select one or more transistors to drive the H-bridge transistors through a capacitor.
An advantage of the present invention is the manufacturer of the HDD can optimize the performance of the head by using the selectable nature of the current overshoot. Optimization could be done for a particular disk drive design, for a specific drive during burn-in, or xe2x80x9con the flyxe2x80x9d when the head is accessing different tracks or sections of the disk platter.